Non-destructive testing (NDT) includes inspection methods which are usually used to search for the presence of defects in components. The types of defects detectable include cracks, porosity, voids, burns, and inclusions. NDT is used by our customers to ensure product integrity and reliability, prevent failure and accidents, ensure customer satisfaction, and maintain a uniform quality level.
Primary methods used by Southwest United Industries are fluorescent penetrant inspection and magnetic particle inspection.
Fluorescent Penetrant Inspection (FPI)
FPI is most commonly used in the inspection of critical machined parts such as aerospace parts. Florescent penetrant inspection consists of applying a fluorescent dye penetrant to the parts to be inspected. The coating has the property to penetrate any emerging crack and after applying an exposure to ultraviolet light the defects or suspect areas will appear as fluorescent light to the trained inspectors’ eyes.
At Southwest the parts are run through a semi-automatic preparation process. The parts are washed and then dried by a drying oven, then immersed in a bath of dye, the dye is then given time to "dwell" so that emerging cracks of corrosion or defective manufacture will contain the penetrating dye which will then show as fluorescent light once exposed to an ultraviolet light source. The parts are examined by one of several level II or level III certified NDT technicians. Southwest’s technicians have many years of experience in examining aviation parts and are able to perform the examination in a thorough and efficient manner.
Magnetic Particle Inspection
Magnetic particle inspection (MPI) is a combination of two nondestructive testing methods: magnetic flux leakage testing and visual testing. Consider a bar magnet. It has a magnetic field in and around the magnet. Any place that a magnetic line of force exits or enters the magnet is called a pole. A pole where a magnetic line of force exits the magnet is called a north pole and a pole where a line of force enters the magnet is called a south pole.
When a bar magnet is broken in the center of its length, two complete bar magnets with magnetic poles on each end of each piece will result. If the magnet is just cracked but not broken completely in two, a north and south pole will form at each edge of the crack. The magnetic field exits the north pole and reenters the at the south pole. The magnetic field spreads out when it encounter the small air gap created by the crack because the air cannot support as much magnetic field per unit volume as the magnet can. When the field spreads out, it appears to leak out of the material and, thus, it is called a flux leakage field.
If iron particles are sprinkled on a cracked magnet, the particles will be attracted to and cluster not only at the poles at the ends of the magnet but also at the poles at the edges of the crack. This cluster of particles is much easier to see than the actual crack and this is the basis for magnetic particle inspection.
The first step in a magnetic particle inspection is to magnetize the component that is to be inspected. Southwest United has modern Magnaflux MPI equipment which can perform multi-directional magnetization as well as demagnetization. If any defects on or near the surface are present, the defects will create a leakage field. After the component has been magnetized, iron particles, either in a dry or wet suspended form, are applied to the surface of the magnetized part. The particles will be attracted and cluster at the flux leakage fields, thus forming a visible indication that Southwest’s experienced level II and Level III certified technicians can detect.
- Magnetic Particle Inspection
- Nital Etch
- Flourescent Penetrant Inspection
View our non-destructive testing facilities.